Abstract [en]

In children with XLH, high circulating levels of FGF23 cause hypophosphatemia with consequent rickets, skeletal deformities, and growth impairment. Conventional therapy consists of multiple daily doses of oral phosphate and active vitamin D (Pi/D). Burosumab is a fully human monoclonal antibody against FGF23 indicated for the treatment of XLH.

In the active-control study CL301 (NCT02915705), 61 children with XLH (1-12 years old) were randomized (1:1) to receive subcutaneous burosumab starting at 0.8 mg/kg every 2 weeks (Q2W) or Pi/D as prescribed by investigators. Eligibility criteria included a Total Rickets Severity Score (RSS) ≥2.0 and prior receipt of Pi/D. The primary endpoint was healing of rickets at Week 40 assessed by radiologists blinded to treatment using the Radiographic Global Impression of Change (RGI-C).